Preheat oven to 450. Halve and peel shallot; finely chop one half. Slice potatoes into 1/4" thick rounds.
Lightly oil a baking sheet. In a large bowl combine potato rounds, 2 tbsp olive oil, garlic powder, salt and pepper; toss until potatoes are coated. Arrange potatoes on the baking sheet into clusters of ~6 rounds (slightly overlapping). Sprinkle each cluster with shredded gruyere. Roast on middle rack for 12 minutes.
Toss green beans with a drizzle of olive oil , salt and pepper on a second baking sheet. Place the beans in the oven when potatoes have reached their 12 minutes - on the top shelf. Leave the potatoes on the middle shelf. Roast for 10-12 minutes.
Pat steaks dry and season with salt and pepper. Heat a large drizzle of oil over medium-high heat. Add steaks and cook until browned (3-6 minutes per side). Transfer steaks to the baking sheet with the green beans - roast until done to your liking (4-7 minutes). Remove beans if they're looking a bit too done before the steaks are done. Set steaks aside to rest.
Wipe out the pan used for browning the steaks. Heat a drizzle of oil over medium heat. Add the shallot - cook until softened (1-2 minutes). Add the sherry vinegar - simmer until it's reduced by half. Stir in 1/3 cup water and the stock concentrate - simmer until thickened. Turn off heat. Stir in sour cream and butter; season with salt and pepper.
Slice steak against the grain; serve with potato clusters and green beans. Top steak with the sauce.
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